Spectroscopic light source



Jan. 30, 1962 A. BARDOCZ 3,

SPECTROSCOPIC LIGHT SOURCE Filed June 16, 1958 3 Sheets-Sheet 2 Jan. 30, 1962 A. BARDOCZ 3,

SPECTROSCOPIC LIGHT SOURCE Filed June 16, 1958 3 Sheets-Sheet 3 INVENTOR ARPAD BARDQ Q7- Uite States atent free 3,019,371 SPECTROSCOPIC LIGHT SOURCE Arpad Bardocz, 4 Qrlay-ntca, Budapest Xi, Hungary Filed June 16, 1958, Ser. No. 742,361 12 Claims. (til. 315-232) This is a continuation-in-part of my copending application, Serial No. 688,694, filed October 7, 1957, now abandoned.

In spectroscopic research Work and spectrochemical analysis the self-ignited or separately ignited spark and interrupted are are frequently employed as light sources. The ignitor spark generator is an important component for separately ignited spark as well as for interrupted arc sources.

The production of sparks is carried out in case of spectroscopic light sources in such a manner that condensers (working condensers) are charged up from the A.C. mains and then discharged through the analytical spark gap (eventually also through controlling spark gap or spark gaps or electron tube connected in series with the analytical spark gap). Igniting sparks discharge in general through a controlling spark gap or controlling tube. To obtain correct operation of the spark source the charging and discharging processes of the condenser should be separated from one another. This is necessary because if during the spark discharge and immediately after it the mains voltage remains on the analytical and controlling spark gaps, in case of higher excitation energies and greater spark frequencies the deionisation of the spark gap is incomplete, consequently the network will be short circuited through them and a regular controlling of the spark discharges can not be maintained. In other words the spark source has to be formed in such a manner that during charging of the condenser no spark discharges shall take place, while during the discharge the condenser shall be completely separated from the network.

Recently a further requirement consists in that at spark sources relative to the moment of given control signal the starting of spark discharges shall take place with a small time scattering (jitter) of an order of magnitude of microsecond, so that consequently spark sources may be applied for the production of time resolved spark spectra. This can be realized by means of electronically controlling spark sources operating with high precision. In connection with the problem the following should yet be noted.

The energy of spark or are discharges applied in some spectroscopic investigations, but first of all in spectrochemical analysis, is not suflicient to produce a spectrum on a photographic plate by a single discharge. For the production of a satisfactory spectrum many hundreds or rather many thousands of discharges are necessary. If the spectrum arising from these discharges is produced in time resolved for instance so that the image of the spark is formed with the aid of a rotating mirror in time resolved on the slit of the spectrograph, than the individual time resolved spark images have to be placed on each other with a very high precision to obtain a high time resolution. Therefore is the high operating precision of the source necessary.

The production of time resolved interrupted arcs as well as the investigation of processes taking place in those are of similar importance. A high precision ignition is needed for the time resolution which might be ensured by an ignitor spark operating with high precision.

The above mentioned requirement-Le. that the charging and discharging process be separated from one another-can be relatively easily met if a number of sparks per second equal to the frequency of the network have to be produced. In this case inserting a rectifier before the working condenser the charging up of the condenser takes place during one of the half cycles of the A.C. network whereas the discharge takes place during the other half cycle when the charged condenser is completely separated from the mains by the rectifier. Hitherto the separation of charging and discharging processes was solved in such a manner in case of some mark sources.

In practical and scientific spectroscopic practice however in general a higher spark frequency than the frequency of the network is desirable. A higher spark frequency results in shorter exposition times and in a higher analytical precision. Moreover it is experimentally proved that the higher the sparking frequency, the higher is the stability of the discharge and consequently the smaller is the time scattering at the production of time resolved spectra. It should be further noted that the timeresolved spectroscopy for routine operation may be in general possible only by a spark frequency higher than the mains frequency. In the majority of cases it is already suflicient if the frequency of the spark discharges is twice the frequency of the A.C. mains.

The subject of the invention consists in such self-ignited or separately ignited low spark and are sources which are also suitable for the production of time resolved spectra, with the aid of which the realization of a spark frequency twice, threefold or sixfold the frequency of the network is feasible in such a manner that the charging and discharging processes of the condenser supplying the excitation energy are completely separated from one another. The self ignited spark sources in question are suitable also for the production of ignitor sparks. The invention includes also such interrupted arc sources which are controlled by the ignitor circuits of the invention, or their working circuit is built according to the invention.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

FIG. 1 is a schematic wiring diagram illustrating the application of the principles of the invention to self-ignited spark sources;

FIG. 2 is a set of curves illustrating the voltage, current, and magnetic induction relations of the transformers in FIGS. 1, 3, and 4;

FIG. 3 is a schematic wiring diagram illustrating a. modified arrangement for controlling the discharge of the condenser;

FIG. 4 is a schematic Wiring diagram illustrating the principles of the invention as applied to the production of separately ignited sparks and arcs;

FIG. 5 is a schematic wiring diagram illustrating an arrangement including a transformer consisting of three units;

FIG. 6 is a schematic wiring diagram illustrating an arrangement for producing sparks for general spectroscopic Work and time-resolved spectroscopic work, and for insuring control of the system in the range of energies and frequencies conventional in spectroscopic practice;

FIG. 7 is a schematic wiring diagram illustrating an alternative embodiment with reference to FIG. 6; and

FIG. 8 is a schematic wiring diagram illustrating a high frequency and high voltage ignitor circuit for controlling separately ignited sparks or interrupted arc sources.

An example of the invention applied to self-ignited spark sources is illustrated in FIGURE 1.. The part of this figure at the left of condenser C is the charging circuit of the spark source, the part at the right the discharge circuit. C is the working condenser storing the excitation energy. Condenser C is charged from the A.C. network through a suitable transformer T and through the full wave rectifier G. The discharging through the analytical spark gap F of the charged condenser C supplying the excitation 3 energy, may take place in different ways. In FIGURE 1 the discharge is realized by the system consisting of electron tube V, or an equivalent component and twin controlling spark gaps S and S Operation of the self-ignited spark source illustrated in FIGURE 1 is as foilows: The core of the secondary coil of transformer T illustrated in FIGURE 1 is possibly of a material of low magnetic saturation, moreover its cross section is small so that the saturation point is already attained for small field intensities. The further increase of the magnetic induction is taken by a shunt magnetic circuit provided with an air gap, or without air gap.

The voltage, current and magnetic induction relations of transformer T of FIGURE 1 are illustrated in FIGURE 2.

In FIGURE 2 a illustrates course in time of the primary voltage, b of the primary current, c of the magnetic induction appearing in the core of the secondary winding and a of the voltage on the secondary terminals of the transformer.

The working condenser C of FIGURE 1 is charged by the voltage impulses of a in FIGURE 2. It should be kept in mind that owing to the presence of the full wave rectifier G all the voltage jumps of d in FIGURE 2 are unidirectional directly before condenser C.

The discharge of condenser C takes place as follows: The charging voltage of condenser C is distributed uniformly by resistances RI and R2 over the symmetric twin controlling spark gaps S and S The twin controlling spark gaps S and S; are so set that in a charged state of condenser C just no break down occurs. By giving in this case from the pulse generator IG onto the grid of the electron tube V otherwise blocked by a negative bias a positive voltage signal, this will conduct and the total charging voltage of condenser C will appear according to the FIGURE 1 on the controlling spark gap S under the influence of which it will break down. Condenser C begins to discharge after the break down takes place through R4-S R3V. During the discharge, the total charging voltage of condenser C will appear on the terminals of resistors R3 and R4. Thus the break down of S or F follows, according to which one of them is shunted through a larger resistance. If as usual in practice-R4 is much larger than R3, the breakdown of S is followed by the breakdown of F.

After this happens, the path of discharge of condenser C will be FS R3-V. After the breakdown of the lower half of twin controlling spark gap S the total charging voltage of condenser C is transferred to resistance R3, i.e. on S Consequently this will break down too. As a result condenser C will discharge freely through the path FSS and supplies the excitation energy.

If under the above mentioned circumstances condenser C is charged by voltage pulses appearing after the rectifier G and the controlling of electron tube V is performed in such a phase position that the discharge takes place in the neighbourhood of the zero value of the descending voltage pulses, for a time no voltage will be present on the terminals of condenser C. Thus the conditions will be favourable for the deionisation of the spark gaps S and S respectively F.

Since FIGURE 2 illustrates with a fairly good approximation the effective conditions the object to separate the charging and discharging phases of working condenser C from one another is practically attained even for a spark frequency corresponding to twice the frequency of the network.

Another example for controlling the discharge of condenser C supplying the excitation energy is illustrated in FIGURE 3. In this figure, F denotes also the analytical spark gap,'while S may be a synchronous rotating interruptor. The phase position of the synchronous interruptor is set as to switch in the neighbourhood of the final zero value of the descending voltage pulse charging 4 condenser C, when condenser C discharges through the spark gaps of the rotating interruptor and the analytical spark gap F.

The electron tube V of FIG. 1, can be replaced by a synchronous interruptor S similar to that shown in FIG. 3. In this case the circuit works as in FIG. 1, only the control of the twin spark gaps S and S will be performed by the rotating interruptor instead of tube V.

If the principle of the invention is to be used for the production of low voltage condensed sparks, for instance the upper circuit of FIGURE 4 shall be employed. I-Iere F denotes the analytical gap. The discharging of working condenser C with the aid of air cored transformer A is carried out by means of the high voltage high frequency currents induced into the circuit CA-F. L1 and L2 in FIGURE 4 are air cored filter coils and their object is to prevent the proceeding into the mains of the high frequency currents circulating in the circuit CA--F. Operation of the circuit in the lower part of FIG. 4 will be described further below.

In spectrochemical analysis and other spectroscopic investigations often interrupted arcs of a very short duration are desirable. The shorter the arcs, the smaller is the cratering in the samples so that the possibility of reproduction is greater and the precision is also higher. In case of sine voltage wave, if not too high voltages are used, the difliculty met with by producing individual arcs of very short duration is, that the arc has to be ignited at the end of the sine Wave, where the voltage is already very low, so that the ignition is rather cumbersome. Interrupted arcs of a very short duration can be produced in the upper circuit illustrated in FIGURE 4 by their safe ignition. In this case the capacity of condenser C is only as great that the high frequency and high voltage currents inducted into the circuit C-AF shall close through them. In this case the excitation energy reaches through transformer T, rectifier G further on choking coils L1 and L2 directly the analytical gap F. Thus the higher ignition voltage and short arcing time is given by itself.

If the circuit illustrated in FIGURE 4 is used for producing interrupted arcs unidirectionally polarised arcs are obtained. Omitting the rectifying element G the polarisation of the arc to be produced becomes two directional.

The aim set is that voltage pulses illustrated in picture I d of FIGURE 2, be as perfect as possible. This can be realized for instance by applying a controllable rectifier triode instead of the rectifying elements in FIGURES 1, 3 and 4, which are somewhat biased. In this case no current will flow through the controllable switches except after having attained a certain voltage threshold, which is, however, higher than the eventual remainder voltage between the voltage pulses. The situation is more simple if, in the circuits of FIGURES 1, 3, and 4, instead of the Graetz rectification a full wave rectification is present, because in the latter case only two controlled rectifier tubes have to be used. Another possibility for producing the more perfect residual voltage pulses between the voltage pulses with a very small voltage consists in using for the transformers of FIGURES 1, 3 and 4 an auxiliary coil or coils. The auxiliary coil in question can be short circuited, can be connected in series with the primary or can be fed separately from a separate supply.

Applying the saturated core transformers described the reactive current uptake from the network may be high with respect to the effective consumption. This might be reduced by applying in the usual way power factor condenser on the network-part of the system.

It is proven by theory and experience that upon applying in FIGURES 1, 3 and 4 instead of transformer T, a transformer of usual layout but provided with saturated core, then the voltage curve of the transformer will be distorted in such a sense that this is from the view point of deionisation of spark gaps favourable respective the charging of the Working condenser after the discharge.

Considering that the magnetizing current of the transformers contains 'overharmonics the possibility is given to produce feed voltage with a frequency corresponding to threefold the number of the frequency of the mains to feed spark or arc sources. Thus if the primary coils of the single phase transformers of FIGURE 5 are connected into star the secondary coils into an open delta and fed from a threephase network, thus from the secondary coils connected into open delta voltage with a frequency corresponding to threefold the frequency of the mains voltage can be taken off. In order to attain this the induction of the iron core has to be chosen high enough so that the overharmonics content of the magnetizing current be great. In FIGURE 5 for example a high voltage spark source is fed from a similar supply. In FIGURE 5, T1, T2 and T3 are three single phase transformers. Working condenser C is charged through rectifier E. The ignition phase of electron tube V has to be set in such a manner that during one half cycle of the feedvoltage of frequency corresponding to threefold of the frequency of the mains condenser C is charged up, and discharged during the other half cycle. In such a manner sparks may be produced with a frequency threefold the frequency of the mains per second. The same result can be achieved with a three-column transformer with saturated core.

A similar solution is shown in FIGURE 6. The coils to which the mains is connected are saturated and placed on cores II, III and IV. On cores I and V the windings supplying the voltage with threefold the mains frequency are placed. The connection of the different coils is shown in the figure as well.

In addition it should be mentioned, that for producing a supply voltage corresponding to threefold the mains frequency a five column transformer type can be usefully applied.

By total separation of the charging and discharging processes a sparking frequency corresponding to sixfold the frequency of the mains can be produced by uniting fo example the transformer system consisting of three units illustrated in FIGURE 5 with the transformer T illustrated in FIGURES 1, 3 and 4. In this case the transformers T1, T2 and T3 are producing the feed voltage of a frequency corresponding to threefold the frequency of the mains, which is then transformed by transformer T illustrated in FIGURES 1, 3 and 4 to the voltage pulses to be seen at d in FIGURE 2. Further details will be understood from the above description.

If, in the case of sources provided with fixed controlling spark gaps, the energy reaching the controlling spark gap or gaps is increased over a certain limit owing to the high level of the discharging energy and of the high sparking frequency, the controlling spark gaps will not deionize until the beginning of the following charging cycle, and thus control of the system might not be maintained. In FIG. 6, such a spark source is illustrated, and wherein control is insured in the range of the energies, respectively frequencies, occurring in usual spectroscopic practice.

In FIG. 6, for instance, condenser C1 is charged through high voltage transformer T, full wave rectifier G, and resistance R1. The working condenser C2 receives its charge from condenser C1 through self-inductance L and ohmic resistance R2. If, in the case of a charged state of condenser C1, there is, with the aid of pulse generator 1G, applied to the grid of the gas filled tube V, blocked by a negative bias, a positive voltage signal, this tube will fire and the charging of condenser C2 begins. The purpose of the ohmic resistance R2, and of selfinductance L, is to limit the current, in the circuit C1--LR2C2V, to the permissible loading of tube V. Condenser C2 is charged to a voltage which corresponds to the breakdown voltage of controlling spark gap S. As soon as the charging voltage of condenser C2 equals the break-down voltage of gap S, the latter breaks down and condenser C2 discharges through the path S-T. T and C3 are coupling members through which the excitation energy reaches the analytical spark gap F.

Care must be taken that, after the break-down of gap S, the supply voltage is effectively disconnected from this gap. This takes place in the following manner: Owing to the design of the system, during the break-down of gap S, condenser C1 has still a considerable charge, which begins to discharge in the form of oscillations over the path L-R2S-TV. Apart from its current limiting role, the inductance L has a secondary role which is to insure the development of oscillation in this circuit. However, this oscillatory discharge will have a duration of only a half cycle of the input frequency, determined by the data of the above-mentioned circuit, since as soon as the current direction changes, the gas filled tube V is extinguished and the network is effectively disconnected from the controlling spark gap S. The insertion of transformer T and condenser C3 is necessary to separate the discharging current of condenser C1 from the analytical spark gap F.

In the case of single phase full wave rectification, the number of sparks produced per second is: twice the fre quency of the supply mains, in the case of the three phase half wave rectification, three times the frequency of the network, and in the case of three phase full wave rectification, six times the frequency of the network. If a large storage condenser is inserted between resistance R1 and the rectifier, an unlimited number of sparks per second may be attained.

In the circuit of FIG. 6, in place of the gas filled tube V, an excitron tube may be employed. This is a controllable triode filled with mercury and which has a mercury cathode.

The excitation energy of self ignited spark sources as well as of the separately ignited spark sources can be stored instead of the working condensers also in artificial lines consisting of condensers and self-inductions. In such cases the artificial line takes the place of working condenser C.

The spark sources of the principle illustrated in FIGS. 1, 3, 5, and 6 can be used also for the ignition of separately ignited sparks respectively for the ignition of interrupted arcs. If the circuits of FIGS. 1, 3, 5, and 6 have to be operated as ignitor circuits, then the ignition energy is transported to the working circuit by means of an air cored transformer by inductive coupling or otherwise. In case of a transmission by air cored transformer in the FIGURES 1, 3, 5, and 6 the primary of the air cored transformer, the primary of the latter takes the place of the analytical spark gap F in the discharging circuit. The lower part of FIGURE 4 serves as an example, where the circuit of FIGURE 1 has been employed as ignitor circuit. In the ignitor circuit of FIGURE -4 the meaning of the reference symbols is the same as in FIGURE 1.

The spark source illustrated in FIG. 6 can also be used as an ignitor circuit as illustrated in FIG. 7.

A further possibility is given for high precision controlling of the separately ignited sparkrespectively interrupted arc sources of FIGURE 4 by high frequency and high voltage igniter currents from the circuit illustrated in FIG. 8. In FIG. 8, the charging of condenser C supplying the ignition energy is carried out through resistance R and the primary coil of air cored transformer A. In figure V denotes a controllable rectifier. In case of a charged state of condenser C giving from pulse generator IG a positive voltage signal onto the grid of rectifier V, this will fire. Through the fired rectifier V and the primary coil of the air cored transformer A, C discharges and supplies the ignition energy.

The circuit according to FIG. 8 can be used as a light source, if, instead of the air cored transformer A, there is used an analytical spark gap shunted by an impedance.

It will be understood from the above that this invention is not limited to the arrangements, devices, steps, conditions and other details specifically described above and illustrated in the drawings and can be carried out with various modifications without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. A spectroscopic light source comprising, in combination, a source of A.C. potential; a device having an input connected to said source and producing, at its output, relatively sharp voltage pulses of short duration in comparison with the duration of a half cycle of said source; full-wave rectifying means connected to the output of said device; an energy storage means in a charging circuit connected to the output of said rectifying means, said rectifying means charging said storage means to peak voltage during each pulse and interrupting the charging current at the end of each pulse while maintaining the storage means charged to peak voltage; an analytical spark gap in series in a power circuit connected across said storage means; and circuit means operatively associated with said power circuit and operable, in synchronized relation with said pulse production, to trigger said power circuit to discharge said storage means across said analytical spark gap just as the voltage of each pulse decays to substantially zero; each charge-discharge cycle of said storage means being effected during a period not exceeding the duration of a half cycle of said source; each of said charging and power circuits being inactive when the other is active.

2. A spectroscopic light source as claimed in claim 1 including twin controlling spark gaps in series with said analytical spark gap in said power circuit; said circuit means including a control network eflfective to successively break down said controlling spark gaps and then to break down said analytical spark gap, during discharge of said storage means.

3. A spectroscopic light source as claimed in claim 2 in which said network includes a grid-controlled electronic valve and an impedance in series with each other and shunting one of said twin controlling spark gaps; said circuit means including impulsing means for said electronic valve.

4. A spectroscopic light source comprising, in combination, a source of A.C. potential; an electromagnetic device having an input connected to said source and producing, at its output, relatively sharp voltage pulses of short duration in comparison with the duration of a half cycle of said source; full-wave rectifying means connected to the output of said device; an energy storage means in a charging circuit connected to the output of said rectifying means, said rectifying means charging said storage means to peak voltage during each pulse and interrupting the charging current at the end of each pulse while maintaining the storage means charged to peak voltage; an analytical spark gap in series in a power circuit connected across said storage means, and circuit means operatively associated with power circuit and operable, in synchronized relation with said pulse production, to trigger said power circuit to discharge said storage means across said analytical spark gap as the voltage of each pulse decays to substantially zero; each charge-discharge cycle of said storage means being effected during a period not exceeding the duration of a half cycle of said source; each of said charging and power circuits being inactivated when the other is active.

5. Spectroscopic light source as claimed in claim 4, in

which the electromagnetic device includes three operatively associated supply transformers having saturated core secondaries.

6. Spectroscopic light source as claimed in claim 4, in which said electromagnetic device includes at least one saturated core supply transformer and the series connection of said gap in said power circuit across said storage means includes a mechanical switch.

7. Spectroscopic light source as claimed in claim 4, in which said electromagnetic device includes at least one saturated core supply transformer and the series connection of said gap in said power circuit across said storage means includes a controllable switch.

8. A spectroscopic light source comprising, in combination, a source of A.C. potential; a saturated core-magnetic shunt transformer having its primary winding connected to said source and producing, at its secondary winding output, relatively sharp voltage pulses of short duration in comparison with the duration of a half cycle of said source; full-wave rectifying means connected to the output of said transformer; an energy storage means in a charging circuit connected to the output of said rectifying means, said rectifying means charging said storage means to peak voltage during each pulse and interrupting the charging current at the end of each pulse while maintaining the storage means charged to peak voltage; an analytical spark gap in series in a power circuit connected across said storage means; and circuit means operatively associated with said power circuit and operable, in synchronized relation with said pulse production, to trigger said power circuit to discharge said storage means across said analytical spark gap just as the voltage of each pulse decays to substantially zero; each charge-discharge cycle of said storage means being effected during a period not exceeding the duration of a half cycle of said source; each of said charging and power circuits being inactive when the other is active.

9. A spectroscopic light source as claimed in claim 8 in which said transformer is provided with auxiliary exciting windings.

10. A spectroscopic light source as claimed in claim 8 in which said transformer is a polyphase transformer.

11. A spectroscopic light source as claimed in claim 10 in which said transformer is provided with auxiliary exciting windings.

12. A spectroscopic light source comprising, in combination, a source of A.C. potential; a device having an input connected to said source and producing, at its output, relatively sharp voltage pulses of short duration in comparison with the duration of a half cycle of said source; full wave rectifying means connected to the output of said device for doubling the number of voltage pulses of the same polarity; an energy storage means in a charging circuit connected to the output of said rectifying means, said rectifying means charging said storage means to peak voltage during each pulse and interrupting the charging current at the end of each pulse while maintaining the storage means charged to peak voltage; an analytical spark gap in series in a power circuit connected across said storage means; and circuit means operatively associated with said power circuit and operable, in synchronized relation with said pulse production, to trigger said power circuit to discharge said storage means across said analytical spark gap just as the voltage of each pulse decays to substantially zero; each charge-discharge cycle of said storage means being effected during a period not exceeding the duration of a half cycle of said source; each of said charging and power circuits being inactive when the other is active.

References ited in the file of this patent 7 UNITED STATES PATENTS Sims et al. Sept. 6, 1955 Barton Mar. 4, 1958 Correspondence Magazine, vol. 33, pages 324 and 325, August 1956. 

